Various methods for swaging needles to sutures are known. Given a needle of a desired gauge, composition and shape, a hole is formed in one end. The hole extends axially into the needle to constitute a suture receptacle and may be formed by mechanical or laser drilling. The term “needle” as used herein is intended to refer to a surgical needle, such that the term “needle” is intended to be a short form of the term “surgical needle” and is synonymous therewith. Typically, the end of the needle having the suture receptacle could be generally described as being in the form of a hollow cylinder, the diameter of the interior hollow of the cylinder being greater than the outside diameter of the suture to be attached to the needle, providing a clearance for insertion of the suture. To attach the suture, a free end of a suture is slidably, axially inserted into the suture receptacle (hole) in the needle and held in that position while a swage die impinges upon the outer peripheral surface of the needle receptacle (the outer surface of the cylinder), collapsing some or all of the cylinder radially inwardly, such that the interior dimensions of the suture receptacle are reduced at some portion thereof. The reduced interior dimensions of the needle receptacle grasp the inserted suture end via mechanical interference and by surface contact (friction). Generally, suture material has some degree of deformability/malleability, but there are limits to same, which, when exceeded, lead to suture material failure. Similarly, there are limits (albeit generally less problematic) to the malleability/deformability/elasticity of needle materials. In swaging, it is desirable to preserve a smooth and continuous exterior needle surface in the area of the suture receptacle. Out of round conditions or sharp edges produced by swaging can increase the drag that the needle experiences when passing through the tissue being sutured, injure the tissue and/or unnecessarily enlarge the hole in the tissue made by the needle as it is passes through the tissue during use. Manufacturing artifacts that protrude from the surface of the needle in the swaging area, (such as “fins”) sometimes occur when the swaging is conducted by a pair of dies which abut one another in the compressed position of a swaging operation. Sharp edges transverse to the axial direction are also sometimes produced by swaging processes at the transition from the uncompressed to the compressed/deformed swaged area of the needle. One approach that has been utilized to provide good suture attachment and smooth outer surfaces in the swaged area is multiple hit swaging, wherein a needle is subjected to swaging of controlled depth, but distributed over a larger area, viz., around the circumference of the needle. To achieve this type of swaging, the needle is rotated (repositioned relative to the swaging dies between multiple swaging compressions. In this manner, multiple angularly offset swaging operations (hits) are performed to attach a single needle to a single suture. While this produces good results, the apparatus used is more complex and expensive than single hit swaging apparatus and the process takes longer. Yet another approach is to use confined stake swaging, wherein the suture receptacle end of a needle to be swaged is inserted between a pair of mating holding dies which, when compressed together, define a substantially cylindrical cavity that grips the needle securely, but does not deform the needle, i.e., the holding dies do not swage the needle. After being gripped by the holding dies, a suture is inserted into the suture receptacle in the needle. One or more elongated swaging elements with one or more staking points (stakes or nibs) slidably extend through the holding dies in mating channel(s) provided therein. When the swaging operation is conducted, the stake(s) are driven into the needle and deform the receptacle end of the constrained needle, such that the needle grips the suture. The holding dies insure that the outer periphery of the needle is supported to allow the stakes to deform the needle in a very localized area without otherwise deforming the receptacle end of the needle. Two adjacent stake swages may be employed to produce two adjacent, inwardly extending dimples/indentations that protrude into the needle receptacle area to capture the suture between the dimples and interior surface of the suture receptacle to grip the suture therebetween. The result is a double stake swaged needle with a pair of indentations but no protrusions, out of round areas or sharp ledges formed as a consequence of swaging.
While double stake swaging produces good results, the process requires a high degree of precision, in particular when used to swage needles to monofilament sutures and to sutures that are made from materials that are sensitive to being pinched off or clipped by the inwardly converging dimples. For example polypropylene is less deformable/malleable than other suture materials, e.g., nylon and tends to be clipped off when subjected to excessive pinching pressure/shear forces. Precision in the formation of the needle diameter, needle hole (and resultant wall thickness), suture diameter, and depth of penetration of the stake swage dies all must be closely controlled to prevent excessive shear force on the suture, while insuring adequate force to provide secure attachment. The precise setup will typically vary for each type of suture/needle combination, requiring reconfiguration of the swaging apparatus for each different product run. During production, testing is used to insure that adequate needle pull-off strength is achieved. Since insuring effective attachment without compromising suture integrity adds significantly to the cost of armed suture production, it remains an objective to make the process easier, more efficient and effective.